The 9-1-1 emergency telephone service makes it simple for an individual to call for help for any kind of emergency. When such a call is placed from a land-line telephone, a 9-1-1 call center can easily determine the caller's location. When a call is placed from a mobile telephone, however, it can be much more difficult to determine the caller's location. Several systems have been implemented or proposed to overcome this difficulty, including the Enhanced 9-1-1 service ordered by the Federal Communication Commission. Other such systems are described in U.S. Pat. Nos. 6,038,438 (Beeson et al.) and 6,314,218 (Chao et al.).
These systems, however, are not fully operative when a call to 9-1-1 fails to connect. As a result, a user's level of safety is diminished when his wireless telephone is out of range. This can make it more difficult for a user to seek help in circumstances where help is needed most—while hiking through a wooded area, or driving along a remote highway, for example.
Safety beacons have been developed that do not rely on the telephone system at all, such as the EPIRB (emergency position-indicating rescue beacon). When it is activated, an EPIRB broadcasts a 406 MHz beacon that is picked up by a satellite. Some EPIRB devices include a GPS (global positioning system) receiver that allows the EPIRB beacon to broadcast its precise location as determined by the GPS receiver. Some EPIRB devices can be carried by an individual and are referred to as PLBs (personal locator beacons). While EPIRB devices have the advantage of near-global coverage, they are intended to be activated only as a last resort, because they can trigger an intense international air-and-sea rescue effort. Moreover, they are typically carried only when a user foresees the possibility of finding himself in peril, as when embarking on an isolated journey over water or through the wilderness. As a result, they are rarely at hand during a more unexpected emergency, such as an accident on a remote stretch of highway.